Breathing abnormalities during sleep are common events in older men and postmenopausal women. Although their etiology remains obscure, a number of observations have been made. First, a reduction in chemosensitivity during sleep is suggested by the hypoxia and hypercapnia seen during sleep disordered breathing and has been demonstrated. Although the explanation for this alteration in ventilatory control is unknown, investigation during wakefulness suggests that respiratory rhythm, resting ventilation, and ventilatory chemosensitivity tend to correlate closely with oxygen consumption (V02) and carbon dioxide production (VC02). As V02-VC02 is reported to be decreased during sleep, we hypothesize that the reduced metabolic rate in sleeping man may be the mediator of not only the decrement in chemosensitivity but also the dysrhythmic breathing. As older men are prone to these disorders, age and gender related variation in sleeping metabolic rate may determine suceptability to sleep disordered breathing. To solidify an association between V02-VC02, chemosensitivity, and breathing during sleep the following studies are planned. Normal men and women between the ages of 20 and 75 years will be studied to determine: a) If disordered breathing occurs in subjects with large decrements in V02-VC02 and not in those maintaining waking levels. b) If episodes of breathing dysrhythmias occur when V02-VC02 is at its lowest level. c) If increasing age is associated with larger sleep induced decrements in V02-VC02 and more breathing abnormalities. d) The effects of testosterone, estrogen, and progesterone on metabolism and breathing during sleep. e) The effects of artifically increasing and decreasing sleeping metabolic rate on breathing pattern. Ventilatory chemosensitivity will also be measured in both groups during sleep to confirm its correlation with metabolic rate. Second, it has been reported that upper airway resistance increases during sleep, probably secondary to decreased airway patency at the level of the pharynx. Although some increase in resistance is likely to occur in everyone due to reduced muscle tone, those people with the smallest hypopharynx seem prone to develop apnea. We plan to measure upper airway patency and resistance during wakefulness in normal men and women, and patients with obstructive sleep apnea to determine: a) If males differ from females; b) If age or weight (obesity) affects upper airway patency; c) The influence of testosterone and other hormones on the upper airway; and d) If people with apnea differ from age, sex, and weight-matched controls. We also hope to determine the relationship between upper airway resistance and breathing disorders during sleep. By such investigation of metabolism, chemosensitivity, and upper airway patency we hope to gain insight into the interactions of these variables in producing apnea and hypopnea during sleep.